In known manner, a turbine engine has a combustion chamber in which air and fuel are mixed prior to being burnt therein. The gas resulting from that combustion flows downstream from the combustion chamber, subsequently feeding a high pressure turbine and a low pressure turbine. Each turbine has one or more rows of stationary airfoils constituting guide vanes alternating with one or more rows of moving airfoils constituting blades (bladed disks or “blisks”), in which the airfoils are spaced apart circumferentially all around the rotor of the turbine. Those turbine airfoils are subjected to the very high temperatures of the combustion gas, which temperatures can reach values that are well above the temperatures that the airfoils in contact with the gas can withstand without damage, which implies that it is necessary to cool them continuously by means of respective integrated cooling circuits, where such a circuit includes multiple cavities when it is desired to provide cooling that is effective and accurate without significantly increasing the flow rate of air and without penalizing the performance of the engine. Hollow airfoils formed in this way are fabricated by the so-called “lost-wax” casting method, which requires the use of a core or model part having an outside surface that matches the inside surface of the finished airfoil, as described in application FR 2 961 552 filed in the name of the Applicant.
In the techniques currently in use, a refractory core made of ceramic is placed in a mold and then a metal or metal alloy is cast between the mold and the core in order to form the airfoil. On cooling, due to the difference in coefficients of thermal expansion for the metal and the core, the metal airfoil shrinks more than the ceramic core, so the ceramic core then exerts forces on the metal airfoil that give rise to stresses therein. With monocrystalline airfoils, the stresses that are induced can lead to recrystallization, which is incompatible with the airfoil being used.
The invention seeks to remedy such drawbacks, at least in part.